What is the difference between a microcontroller and a PC?

With the development of society and the increase in demand, computers are also constantly updating and developing. Since the emergence of computers is due to numerical calculations, electronic computer technology has long been developed along the path of satisfying large-scale high-speed numerical calculations. It was not until the 1970s that electronic computers showed extraordinary functions in digital logic operations, reasoning, automatic control, etc., and various control fields began to put forward completely different requirements for the development of computer technology from traditional large-scale high-speed calculations. These requirements are: facing the control object, facing various sensor 
signals  , facing human-computer interactive operation control, and being able to be easily embedded in industrial control application systems.
In order to achieve the above requirements, in recent years, single-chip microcomputers (abbreviated as single-chip microcomputers) have come into being. Single-chip microcomputers are also called "microcontrollers" and "embedded microcontrollers." The term single-chip microcomputer was originally "SingleChipMicrocomputer", abbreviated as SCM. When the single-chip microcomputer was born, SCM was an accurate and popular name, and the term "single-chip microcomputer" accurately expressed this concept. As SCM continues to expand its control functions in technology and architecture, the single-chip microcomputer can no longer be accurately expressed by "single-chip microcomputer". Internationally, "MCU" (Micro Controller Unit) is gradually being used instead, forming a term recognized and eventually unified by the microcontroller community. In China, the term "single-chip microcomputer" has become a convention, so it continues to be used. 
What exactly is a single-chip microcomputer? It is a computer, but it is miniature. Although it is small, it has all the necessary functions: it also uses modules similar to those of a computer, such as CPU, memory, parallel bus, and storage devices with the same functions as hard disks. The difference is that the performance of these components is much weaker than that of our home computers, but the price is also low, generally not more than 10 yuan... It is enough to use it to do some not very complicated work such as controlling electrical appliances. We can see it in the fully automatic drum washing machines, exhaust hoods, VCDs and other home appliances we use now!... It is mainly used as the core component of the control part. 
It is an online real-time control computer. Online means on-site control, which requires strong anti-interference ability and low cost. This is also the main difference from offline computers (such as home PCs). 
Single-chip microcomputers rely on programs and can be modified. Different programs can achieve different Different functions, especially some special and unique functions, which other devices need to spend a lot of effort to achieve, and some are difficult to achieve even with great effort. If a not very complex function is solved by pure hardware such as the 74 series developed in the 1950s in the United States, or the CD4000 series in the 1960s, the circuit must be a large PCB board! But if it is a series of single-chip microcomputers successfully launched in the market in the 1970s in the United States, the result will be very different! Just because the single-chip microcomputer can achieve high intelligence, high efficiency, and high reliability through the program you write! 
Since the single-chip microcomputer is sensitive to cost, the dominant software is still the lowest-level assembly language, which is the lowest-level language above binary machine code. Since it is so low-level, why should it be used? Many high-level languages ​​have reached the level of visual programming. Why not use it? The reason is very simple, that is, the single-chip microcomputer does not have a CPU like a home computer, nor does it have a massive storage device like a hard disk. Even if there is only one button in a small program written in a visual high-level language, it will reach a size of tens of K! It is nothing for the hard disk of a home PC, but it is unacceptable for a single-chip microcomputer. The utilization rate of hardware resources of single-chip microcomputers must be very high, so although the assembly language is primitive, it is still widely used. In the same way, if the operating system and application software on a giant computer are brought to a home PC to run, the home PC will not be able to bear it.